It is often desirable to mark tissue with a marker so that it can later be identified. For example, tissue may be sampled by performing a biopsy to remove a small portion of the tissue. If the biopsy site is marked, the marker may later be used to guide a doctor or health care professional in returning to the site of the biopsy, should further medical procedures need to be performed at this site. For example, tissue (including small masses or microcalcifications) is sometimes completely removed by procedures such as stereotactic core biopsy. Often during these procedures, a metal clip is employed through the biopsy needle to mark the target. Should another procedure be required in the same area (e.g. a further excision or biopsy), the metal clip acts as a marker to aid in re-identification of the target or target region. The marker may also be used to confirm that the biopsied site matches the intended target.
Unfortunately, there are many problems with currently available markers such as the metal clips mentioned above. In particular, markers such as metal clips may move (or migrate) from the correct or initial position. Furthermore, the size and shape of these metal clips or other markers is limited because they must typically fit within the small diameter of a delivery needle. Finally, there may be problems identifying the marker once it has been inserted.
Migration of tissue markers is a well-described phenomenon, which can cause serious problems with patient treatment. Migration may occur immediately after insertion, or it may occur some time after insertion, and may have many causes. One common cause of clip migration occurs when the tissue (e.g., breast tissue) re-expands after compression or pressure on the tissue is released, for example, when the biopsy procedure is completed. This may be referred to as the “accordion effect.” Markers may also be displaced after being inserted into the tissue by formation of a hematoma, because the marker (particularly smaller markers) may “float” within the hematoma.
Most currently available tissue markers are also limited to visualization (or localization) by a single imaging modality. For example, metal clip markers may be radioopaque and therefore visible by X-ray based modalities, but may not be visualized by ultrasound or other modalities. Furthermore, imaging of a tissue marker may also be limited by the size or shape of the marker, because the size and shape of most currently available markers are constrained by the insertion mechanism. For example, markers that are inserted through a biopsy needle generally have a cross-sectional dimension that is smaller than the diameter of the biopsy needle even after they have been inserted into the body.
Exemplary tissue markers have been described in U.S. Pat. No. 6,228,055 to Foerster et al., U.S. Pat. No. 6,261,243 to Burney et al., U.S. Pat. No. 6,350,244 to Fisher, U.S. Pat. No. 6,234,177 to Barsch, and U.S. Pat. No. 6,371,904 to Sirimanne et al. Each of these references is incorporated in its entirety herein. However, none of these devices adequately addresses all of the concerns described above.
Applicants have recognized that it would be desirable to provide a relatively large tissue marker that is deliverable in a smaller profile sheath, embodiments of which are described herein along with methods of making same.